Emoticons (or emoji) are considered colloquial and so are not suitable for general business communication, including as E-mails to customers, senior management or other employees you do not know personally.
Emoticons may be suitable for your own team or other employees you have a close relationship with. It comes down to company culture. Many software companies, for example, are quite informal and accept them. Old, traditional law firms may view them as trite and unprofessional.
Emoticons are more suitable in less formal communication such as messaging or chat apps (although be aware these still are considered legal correspondence and so all the legal rules with E-mail still apply) compared to more formal E-mails. Younger employees are also more inclined to accept and use them.